During George III's reign, his home country was defeated in a noble war and he lost control of the United States of America. His two kingdoms Great Britain and Ireland were merged into the United Kingdom of Great Britain and Ireland. Also during his reign Great Britain and its successor the United Kingdom were at war with republican and Napoleonic France. His land in Hanover, Germany became a Kingdom. He suffered from periodic bouts of insanity. One of these caused a Regency crisis in 1788 during which the kingdom of Ireland attempted unsuccessfully to nominate his son George IV as regent. He quickly recovered and prevented this.[1]

George III signed the Quebec Act of 1774 abolishing William of Orange's anti-Roman Catholic laws in Great Britain's 13 North American colonies.[2][3] Also during his reign George III signed legislation abolishing some of the anti-Catholic Laws in Great Britain and Ireland, such as Catholic Relief Acts of 1772 and 1774 allowing Roman Catholics to have land leases in Great Britain, and a 1793 Irish Parliament bill called Hogart's Act allowing Roman Catholics to vote in Irish elections. But he still blocked a proposal in 1800 by the British Parliament to allow Catholics to sit in Parliament.[4]

In the later part of his life, George III suffered from recurrent, and eventually permanent, mental illness. Although it has since been suggested that he suffered from the genetic blood disease porphyria, the cause of his illness is not certain. After a final relapse in 1810, a regency was established, and George III's eldest son, George, Prince of Wales, ruled as Prince Regent. On George III's death, the Prince Regent succeeded his father as George IV.

Because of "his plain, homely, thrifty manners and tastes", George III has been nicknamedFarmer George.